1. Field of the Invention
The present invention relates to a construction in which spark plugs, ignition coils and fuel injectors are arranged in a multi-cylinder internal combustion engine with an intake manifold having branch pipes connected to one side of a cylinder head and curved on the one side of the cylinder head to thereby allow the manifold to extend to directly above a cylinder-head cover.
2. Description of the Related Art
Conventionally, in order to achieve a compact arrangement of an intake manifold, there has been proposed a multi-cylinder internal combustion engine in which branch pipes of an intake manifold are curved to thereby allow the intake manifold to extend to directly above a cylinder-head cover, and an example thereof is disclosed in JP-A-10-176543. In this disclosed internal combustion engine, the intake manifold which is connected to a side of a cylinder head is curved at a side of the cylinder-head cover to extend upwardly, and is connected to a surge tank provided directly above the cylinder-head cover. The surge tank is then disposed directly above ignition coils which are provided at a substantially central location on the cylinder-head cover in a direction normal to a direction in which cylinders are arranged as viewed from a direction of axes of the cylinders.
Incidentally, in the prior art, the ignition coils are provided at the central location of the cylinder-head cover, and moreover, the surge tank is disposed directly above the ignition coils so disposed. Therefore, the surge tank is positioned higher over the cylinder-head cover by such an extent that the ignition coils protrude upwardly from the cylinder-head cover along the axes of the cylinders, thereby causing a problem that the overall height of the internal combustion engine is so increased. In addition, servicing the ignition coils requires the removal of the surge tank, thereby causing another problem that the efficiency of servicing work is deteriorated.
The invention was made in view of these situations, and a common object of first to fourth aspects of the invention is to provide a compact multi-cylinder internal combustion engine by maintaining as low as possible in a direction of axes of cylinders the height of a multi-cylinder engine in which an intake manifold is allowed to extend to directly above a cylinder-head cover. Furthermore, an object of the second and fourth aspects of the invention is to improve the workability in servicing the ignition coils.
An object of the third aspect of the invention is to provide a multi-cylinder internal combustion engine which is made compact in the cylinder arrangement direction.
According to the first aspect of the invention, there is provided a multi-cylinder internal combustion engine comprising a cylinder head attached to the top of a cylinder block in which a plurality of cylinders are formed, a cylinder-head cover attached to the top of the cylinder head, an intake manifold having a plurality of branch pipes connected to one side of the cylinder head:and curved on the one side of the cylinder head to thereby allow the intake manifold to extend to directly above the cylinder-head cover, a valve train chamber formed by the cylinder head and the cylinder-head cover and spark plugs and fuel injectors respectively incorporated in the cylinder head, the multi-cylinder internal combustion engine being characterized in that the spark plugs are disposed outside the valve train chamber on a side of the valve train chamber where curved portions of the plurality of branch pipes are disposed, and in that the fuel injectors and ignition coils that are provided above the spark plugs are disposed between the valve train chamber and the curved portions of the plurality of branch pipes in a direction normal to axes of the cylinders as viewed from a direction in which the cylinders are arranged.
According to the construction of the first aspect of the invention, the following advantages are provided. Namely, since the spark plugs are disposed outside the valve train chamber and on the side of the valve train chamber where the curved portions of the branch pipes are disposed, the spark plugs can easily be attached to or detached from the cylinder head. Moreover, since the fuel injectors and ignition coils are disposed between the valve train chamber and the curved portions of the branch pipes in the direction normal to the axes of the cylinders as viewed from the cylinder arrangement direction, the ignition coils are in no case positioned directly above the cylinder-head cover and therefore the intake manifold can be disposed closer to the cylinder-head cover in the direction of the axes of the cylinders, so that the dimension of the internal combustion engine can be reduced in the cylinder-axis direction by the extent that the intake manifold is disposed closer to the cylinder-head cover, whereby the internal combustion engine can be made compact in the cylinder-axis direction. Moreover, it also contributes to the accomplishment of the compact internal combustion engine to make use of the space formed by the curved portions of the branch pipes in the direction normal to the cylinder-axis direction for the disposition of the fuel injectors and ignition coils.
According to the second aspect of the invention, there is provided a multi-cylinder internal combustion engine as set forth in the first aspect of the invention, wherein the ignition coils are disposed in such a manner that the ignition coils do not overlap the branch pipes respectively as viewed in a direction in which the ignition coils are attached to or detached from the cylinder head.
According to the construction of the second aspect of the invention, in addition to the advantages provided by the first aspect of the invention, the following advantage is provided. Namely, since the ignition coils are disposed in such a manner that the ignition coils do not overlap the branch pipes respectively as viewed in a direction in which the ignition coils are attached to or detached from the cylinder head, in servicing the ignition coils, the ignition coils can be detached from and then attached to the cylinder head without removing the intake manifold, thereby improving the workability in servicing the ignition coils.
According to the third aspect of the invention, there is provided a multi-cylinder internal combustion engine as set forth in the first or second aspect of the invention, wherein the ignition coils are disposed, respectively, by one side of portions of the branch pipes whose outside diameters in the direction in which the cylinders are arranged are made smaller.
According to the construction of the third aspect of the invention, in addition to the advantages provided by the cited aspects of the invention, the following advantage is provided. Namely, since the ignition coils are disposed, respectively, by one side of portions of the branch pipes whose outside diameters in the direction in which the cylinders are arranged are made smaller, the total width for each cylinder in the cylinder arrangement direction which includes the ignition coil and the branch pipe is reduced, whereby the cylinder head can be made compact in the cylinder arrangement direction.
According to the fourth aspect of the invention, there is provided a multi-cylinder internal combustion engine as set forth in any of the first to third aspects of the invention, wherein the ignition coils each have a mounting portion to the cylinder-head cover and a connecting portion where a connecting terminal is connected for supplying electric current, and wherein the connecting portion is disposed in such a manner that the connecting portion does not overlap the branch pipe as viewed in a direction in which the connecting terminal is attached to or detached from the cylinder-head cover and is located on an opposite side of the ignition coil to a side thereof where the mounting portion is provided as viewed in the direction in which the connecting terminal is attached to or detached from the cylinder-head cover.
According to the construction of the fourth aspect of the invention, in addition to the advantages of the cited aspects of the invention, the following advantage is provided. Namely, since the ignition coils are disposed between the valve train chamber and the curved portions of the branch pipes in the direction normal to the axes of the cylinders as viewed from the cylinder arrangement direction, and since the connecting portion is disposed in such a manner that the connecting portion does not overlap the branch pipe as viewed in the direction in which the connecting terminal is attached to or detached from the cylinder-head cover and is located on an opposite side of the ignition coil to a side thereof where the mounting portion is provided as viewed in the direction in which the connecting terminal is attached to or detached from the cylinder-head cover, in any case there is provided no disturbance by the branch pipes and the cylinder head in attaching and detaching the connecting terminals to and from the connecting portions of the ignition coils, so that the attachment and detachment of the connecting terminals to and from the connecting portions of the ignition coils is facilitated, thereby improving the workability in detaching and attaching the connecting terminals from and to the ignition coils in servicing the same.